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Old 11-18-2013, 07:26 PM   #1
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Motor noise vs fan noise vs overdrive question

Have a 1991 300LE, and found out after I got it that it has overdrive (really cool!). I found out by getting it going rather fast one day, everything got really quintet all of a sudden...it was like warp drive! Having done some research, I think I have a 4L80E transmission. Problem is, OD only kicks in at 65 and this is faster than I usually drive unless I'm on a wide open highway. As soon as I drop down to 60 or 55, I get much more noise from the motor. I can't tell if it's dropping out of OD or if it's a fan...?
Does anyone know how I can get that nice quiet OD cruise at 55 mph? Thanks, Sebastian
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Old 11-18-2013, 08:29 PM   #2
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Higher gearing in the rear axle. You probably have something like 4.10 gears, you could go with, say 4.50. Get quicker pick-up off the line, to boot.
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Old 11-18-2013, 09:18 PM   #3
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4.5 would be a lower gear. Higher numerically means lower gearing.
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Old 11-19-2013, 06:26 AM   #4
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Make sure the TV,(throttle valve) cable is adjusted properly, no slack, but little tension usually does it. May take several road tests.
A lot of folks call it the "kick down" cable...rong.

It's the bottom cable in this stock photo.


Check the fan clutch for the roar sound, should only "roar" with engine hot, spin free with engine cold, not running.

Bob
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Old 11-19-2013, 06:35 AM   #5
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Semantics...

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Originally Posted by ROBERT CROSS View Post
Make sure the TV,(throttle valve) cable is adjusted properly, no slack, but little tension usually does it. May take several road tests.
A lot of folks call it the "kick down" cable...rong.

It's the bottom cable in this stock photo.


Check the fan clutch for the roar sound, should only "roar" with engine hot, spin free with engine cold, not running.

Bob
I was always told that was the detent cable. It moves the valve body in the transmission to change shift points. A 4L80E should not have one, since it's electronically controlled.
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Old 11-19-2013, 07:00 AM   #6
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Ah yes 700r4...lost track of time again.

Pressure test in order.

Bob
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Old 11-19-2013, 09:30 PM   #7
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So, a transmission shop can't remap the transmission controller to kick in OD at a lower speed?

I could see the fan clutch turning off at a higher speed due to increased cooling, but it seems odd that it would kick back on at 55 and off at 65...does not sound temp related, but the noise sounds fan related. I guess I could replace the fan clutch and see if that makes a difference.

Thanks for the feedback
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Old 11-19-2013, 10:52 PM   #8
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I'm curious if you have a tachometer? That would be the easiest way to tell if the trans is dropping out of OD. Temperature change would indicate the fan clutch engaging.

I'm more old school but I would think the trans shift points could be adjusted by linkage adjustment or computer re-map or a combination of both.
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Old 11-20-2013, 06:49 AM   #9
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Question

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So, a transmission shop can't remap the transmission controller to kick in OD at a lower speed?

I could see the fan clutch turning off at a higher speed due to increased cooling, but it seems odd that it would kick back on at 55 and off at 65...does not sound temp related, but the noise sounds fan related. I guess I could replace the fan clutch and see if that makes a difference.

Thanks for the feedback
Are you sure of your chassis year? You may be on the cusp of a tranny change.
You may have a 91 AS with a 89-90 chassis. Ck the linkage.

Ck fan cold & after warm-up, ck how difficult the fan is to rotate. Easy cold difficult warm.

Bob
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Old 11-24-2013, 11:19 PM   #10
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My chassis is a 1990, and I guess the trams with OD came put in 1991, but I don't know if that would be "model year" so same as mine, but I'm convinced I have the OD. I got her out for a drive today, and same thing...up to 60- 65mph and it gets really quiet. I don't see a drop in rpm, and when I get back down to 55 or 50, the noise starts up again. What's weird is it seems speed or rpm related as the temp is not really changing. I also tried really putting the boots to it off the line as had not tried this yet...for some reason, it ran quite in the lower gears for a short while?!? I have an electric fan on the front as well. I have not figured when that comes on, or if it's on a thermostat. I guess I could unplug it next time I go out. Always an adventure.
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Old 11-24-2013, 11:36 PM   #11
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The 4l80e has 17 bolts...will count next time I'm on location.
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Old 11-25-2013, 07:45 AM   #12
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The electric fan should come on when the engine reaches a specific temp controlled by a sensor and/or when the AC is on.
The fan clutch is on the engine cooling fan, behind the radiator. The fan should spin free with little resistance with a cold engine. If it's hard to spin it will roar on acceleration and be somewhat quieter at lower cruising rpm's.

Do you have a second cable attached to the the throttle linkage?
A lock-up torque converter can feel like OD but will not drop the RPM's.

Bob
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Old 11-25-2013, 10:37 PM   #13
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Hi Bob, I have a second cable, but it's for the cruise control.
Lockable-up torque converter eh? I had to read up on that one, and I think you are correct!
Now I wonder why it only kicks in at such a high speed, and how can I get it down to 55? I will see if a transmission shop can adjust it. I also read there are a couple sensors that can be cleaned and throttle position sensor calibrated.

The Powertrain Control Solutions Simple Shift TCU also looks like a good solution...
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Old 11-26-2013, 06:03 AM   #14
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It's easy to tell the difference between cables. The cruise cable will attach at the same point at or near the throttle cable.
The TV cable attaches at a point on the linkage that sends throttle position information the the transmission.

The TV cable gets pulled, the cruise cable does the pulling.




Bob
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